As environmental problems continue to grow, there is an increased need for ecologically compatible materials on the polymer market. Attempts to take account thereof have resulted in the use of products from fermentatively produced polyesters, polyvinyl alcohols, starch and starch derivatives with a low degree of substitution, cellulose and cellulose derivatives as well as blends of these with conventional plastics, such as polyethylene. Those materials have a drawback in that they have insufficient durability, inferior mechanical properties, and, especially in the case of blends with conventional plastics, they are but incompletely biodegradable. Using derivatized starch, especially with a higher degree of substitution and modified with appropriate biodegradable plasticizers (DE 41 14 185), materials were achieved which are readily processed thermoplastically and are useful for injection molding, melt-spinning or the preparation of films. However, these materials are known to become brittle again rather soon.
According to the German Laid-Open No. 43 26 118, such brittleness can be prevented by modifying starch esters with a degree of substitution of &lt;3, preferably from 1.8 to 2.6, using polyethylene glycol (PEG). According to the German Laid-Open No. 44 18 678, it is possible to increase melt stabilization of blends from starch esters with a degree of substitution of &lt;3 and polyalkylene glycols and to improve their biodegradability by the addition of aliphatic, saturated or unsaturated, dicarboxylic acids and/or oxydicarboxylic acids and/or oxytricarboxylic acids.
However, such blends have insufficient water stability and mechanical properties, in particular elongation at break, impact resistance, and barrier characteristics, particularly in the case of molding compositions which are to be processed by injection molding, deep drawing, melt-spinning and extruding, especially into films.
Packages for cigarettes and other tobacco products are known in a variety of designs and made of a number of rather different materials, such as pouches, cans and hinged-lid boxes made of aluminum, tin, cardboard or plastic. The most widely spread package for cigarettes is the hinged-lid box according to DEP 34 14 214 (U.S. Pat. No. 5,379,889). This package achieves the required protection of its contents by a multi layer combination of different materials. It frequently consists of an inner layer of backed or printed aluminum foil, a cardboard or paper layer which in most cases is printed with specifications, and an outer closed wrapping of a thermally weldable film, e.g. of polypropylene (German Laid-Open Nos. 30 27 448 and 28 44 238). Other packages for cigarettes achieve the required protection of their contents from deformation, flavor and humidity losses by the combination of other materials, such as tin (i.e. metal sheet) and paper according to EP 087 483.
However, packages have also been described which exclusively consist of films of thermoplastics (German Laid-Open No. 42 26 640).
In order to improve the mechanical properties and the gas and water vapor permeability of thermoplastic films used for cigarette packages, plastic films of polypropylene or polyalkylene terephthalate are used which have been oriented by biaxial stretching and may be metallized (German Laid-Open No. 36 32 276, EP 454 003, EP 317 818).
All these solutions have drawbacks in that protection of the contents as well as water vapor and gas tightness can only be achieved if materials are selected comprising at least one aluminum foil, tin foil, or biaxially stretched plastic film. The necessary specifications are printed mostly onto a cardboard, tin or paper wrapping used in said combination. These complex packages require considerable expenditures for their preparation as well as for the packing material employed in order to maintain the quality of the packaged goods and to ensure the appeal of the package.
After use, the packages usually go to the waste and therefore contribute to the existing environmental problems. They decompose but very slowly or not at all when under weathering actions on dumping grounds and in nature. Their being reprocessed in the usual recycling processes requires that the materials be first separated. Such separation can be performed but incompletely in general. Moreover, these processes are adversely affected, e.g. by contamination of the process water. Reuse of the packages is out of the question for food law reasons.